char_dev.c里的中文注释,仅代表个人理解,仅供参考。如有错误之处,请指出,谢谢!
1 /* 2 * linux/fs/char_dev.c 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 */ 6 7 #include <linux/init.h> 8 #include <linux/fs.h> 9 #include <linux/kdev_t.h> 10 #include <linux/slab.h> 11 #include <linux/string.h> 12 13 #include <linux/major.h> 14 #include <linux/errno.h> 15 #include <linux/module.h> 16 #include <linux/smp_lock.h> 17 #include <linux/seq_file.h> 18 19 #include <linux/kobject.h> 20 #include <linux/kobj_map.h> 21 #include <linux/cdev.h> 22 #include <linux/mutex.h> 23 #include <linux/backing-dev.h> 24 25 #ifdef CONFIG_KMOD 26 #include <linux/kmod.h> 27 #endif 28 #include "internal.h" 29 30 /* 31 * capabilities for /dev/mem, /dev/kmem and similar directly mappable character 32 * devices 33 * - permits shared-mmap for read, write and/or exec 34 * - does not permit private mmap in NOMMU mode (can't do COW) 35 * - no readahead or I/O queue unplugging required 36 */ 37 38 struct backing_dev_info directly_mappable_cdev_bdi = { 39 .capabilities = ( 40 #ifdef CONFIG_MMU 41 /* permit private copies of the data to be taken */ 42 BDI_CAP_MAP_COPY | 43 #endif 44 /* permit direct mmap, for read, write or exec */ 45 BDI_CAP_MAP_DIRECT | 46 BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP), 47 }; 48 49 static struct kobj_map *cdev_map; 50 51 static DEFINE_MUTEX(chrdevs_lock); 52 53 static struct char_device_struct { 54 struct char_device_struct *next; 55 unsigned int major; 56 unsigned int baseminor; 57 int minorct; 58 char name[64]; 59 struct file_operations *fops; 60 struct cdev *cdev; 61 /* will die */ 62 } *chrdevs[CHRDEV_MAJOR_HASH_SIZE]; 63 64 /* index in the above */ 65 static inline int major_to_index(int major) 66 { 67 /* [CGW]: 根据主设备号,转换成对应的索引 68 * 即主设备号就是索引号 69 */ 70 return major % CHRDEV_MAJOR_HASH_SIZE; 71 } 72 73 #ifdef CONFIG_PROC_FS 74 75 void chrdev_show(struct seq_file *f, off_t offset) 76 { 77 struct char_device_struct *cd; 78 /* [CGW]: 根据offset (相当于索引),找到对应设备 */ 79 if (offset < CHRDEV_MAJOR_HASH_SIZE) { 80 /* [CGW]: 上锁 */ 81 mutex_lock(&chrdevs_lock); 82 /* [CGW]: 打印该设备项下链表中所有节点的主设备号,和设备名 */ 83 for (cd = chrdevs[offset]; cd; cd = cd->next) 84 seq_printf(f, "%3d %s\n", cd->major, cd->name); 85 /* [CGW]: 解锁 */ 86 mutex_unlock(&chrdevs_lock); 87 } 88 } 89 90 #endif /* CONFIG_PROC_FS */ 91 92 /* 93 * Register a single major with a specified minor range. 94 * 95 * If major == 0 this functions will dynamically allocate a major and return 96 * its number. 97 * 98 * If major > 0 this function will attempt to reserve the passed range of 99 * minors and will return zero on success.100 *101 * Returns a -ve errno on failure.102 */103 104 static struct char_device_struct *105 __register_chrdev_region(unsigned int major, unsigned int baseminor,106 int minorct, const char *name)107 108 {109 struct char_device_struct *cd, **cp;110 int ret = 0;111 int i;112 113 /* [cgw]: 分配一块char_device_struct大小的内存块 */114 cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);115 /* [cgw]: 分配失败 */116 if (cd == NULL)117 return ERR_PTR(-ENOMEM);118 /*[cgw]: 上锁,进入临界区*/119 mutex_lock(&chrdevs_lock);120 /* temporary */121 /*[cgw]: 如果主设备号为0,则从最大的设备号开始,往下查找第一个未被122 *注册的设备123 */124 if (major == 0) {125 /*[cgw]: 从大到小开始查找*/126 for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {127 /* [cgw]: 找到第一个未被注册的设备 */128 if (chrdevs[i] == NULL)129 break;130 }131 /* [cgw]:未找到空位 */132 if (i == 0) {133 ret = -EBUSY;134 goto out;135 }136 /* [cgw]: 以该空位的序号为主设备号 */137 major = i;138 ret = major;139 }140 141 /* [cgw]: 手工分配一个主设备号,和次设备号基址 */142 cd->major = major;143 /* [cgw]: 手工分配次设备号基址 */144 cd->baseminor = baseminor;145 /* [cgw]: 分配minorct个次设备号 */146 cd->minorct = minorct;147 /* [cgw]: 分配设备名 */148 strncpy(cd->name,name, 64);149 /* [cgw]: 找到主设备号在设备列表中的索引 */150 i = major_to_index(major);151 /* [cgw]: 当前分配的设备号比较设备列表,判断该设备号是否152 * 合法153 */154 for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)155 /* [cgw]: 当前分配的主设备号,小于该主设备号索引对应的,设备列表156 * 中的主设备号,合法157 * 这个里有点不解,从i = major_to_index(major);看出,主设备号和该主158 * 设备号对应的索引是相等的,为什么(*cp)->major > major是合法呢159 */160 if ((*cp)->major > major ||161 /* [cgw]: 当前分配的主设备号,等于该主设备号索引对应的,设备列表162 * 中的主设备号,并且符合以下条件之一,当前分配的次设备号,等于163 * 小于该主设备号索引对应的,设备列表中的次设备号。或者,当前分164 * 配的次设备号,小于该主设备号索引对应的,设备列表中的次设备基165 * 址以后minorct个次设备号166 */167 ((*cp)->major == major &&168 (((*cp)->baseminor >= baseminor) ||169 ((*cp)->baseminor + (*cp)->minorct > baseminor))))170 break;171 /* Check for overlapping minor ranges. */172 /* [cgw]: 当前分配的主设备号,等于该主设备号索引对应的,设备列表173 * 中的主设备号,判断次设备号是否在范围内174 */175 if (*cp && (*cp)->major == major) {176 int old_min = (*cp)->baseminor;177 int old_max = (*cp)->baseminor + (*cp)->minorct - 1;178 int new_min = baseminor;179 int new_max = baseminor + minorct - 1;180 181 /* New driver overlaps from the left. */182 if (new_max >= old_min && new_max <= old_max) {183 ret = -EBUSY;184 goto out;185 }186 187 /* New driver overlaps from the right. */188 if (new_min <= old_max && new_min >= old_min) {189 ret = -EBUSY;190 goto out;191 }192 }193 194 /* [cgw]: 新加入的设备, 添加到该主设备号链表 */195 cd->next = *cp;196 /* [cgw]: 设备列表指针指向新加入设备*/197 *cp = cd;198 /* [cgw]: 解锁,退出临界区*/199 mutex_unlock(&chrdevs_lock);200 return cd;201 out:202 203 /* [cgw]: 解锁,退出临界区*/204 mutex_unlock(&chrdevs_lock);205 /* [cgw]: 释放为新设备创建的内存*/206 kfree(cd);207 return ERR_PTR(ret);208 }209 210 static struct char_device_struct *211 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)212 213 {214 struct char_device_struct *cd = NULL, **cp;215 /* [CGW]: 根据主设备号,找出该主设备号所在列表中的索引*/216 int i = major_to_index(major);217 /* [CGW]: 上锁,进入临界区 */218 mutex_lock(&chrdevs_lock);219 /* [CGW]: 根据索引,找出该主设备号所在列表项 */220 for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)221 /* [CGW]:主设备号所在列表项中, 在主设备号对应的链表中,查找判断该主设备号,222 * 次设备号基址,次设备号个数是否已经被注册223 */224 if ((*cp)->major == major &&225 (*cp)->baseminor == baseminor &&226 (*cp)->minorct == minorct)227 /* [CGW]: 已经被注册,停止查找 */228 break;229 /* [CGW]: 主设备号所在链表中的节点230 * (注意: 设备列表中,每个设备号都对应一个链表,该链表用于存放此设备号) 231 */232 if (*cp) {233 /* [CGW]: 取出该节点 */234 cd = *cp;235 /* [CGW]: 更新cp,指向下一个节点*/236 *cp = cd->next;237 }238 239 /* [CGW]: 解锁,退出临界区 */240 mutex_unlock(&chrdevs_lock);241 /* [CGW]: 返回该设备(节点) */242 return cd;243 244 }245 246 247 248 249 /**250 * register_chrdev_region() - register a range of device numbers251 * @from: the first in the desired range of device numbers; must include252 * the major number.253 * @count: the number of consecutive device numbers required254 * @name: the name of the device or driver.255 *256 * Return value is zero on success, a negative error code on failure.257 */258 259 int register_chrdev_region(dev_t from, unsigned count, const char *name)260 261 {262 struct char_device_struct *cd;263 dev_t to = from + count;264 dev_t n, next;265 /* [CGW]: 分配count个连续的设备 */266 for (n = from; n < to; n = next) {267 /* [CGW]: 主设备号+1递增 */268 next = MKDEV(MAJOR(n)+1, 0);269 if (next > to)270 next = to;271 272 /* [CGW]: 根据主、次设备号基址,分配next - n个连续次设备号的设备,273 * 并根据主设备号分配设备名274 * 如果MINOR(n)为0,next-n的值应恒为256,未验证!!!275 */276 cd = __register_chrdev_region(MAJOR(n), MINOR(n),277 next - n, name);278 /* [CGW]: 分配失败 */279 if (IS_ERR(cd))280 goto fail;281 }282 return 0;283 284 fail:285 286 /* [CGW]: 当前分配到了第n个设备就失败了*/287 to = n;288 /* [CGW]: 注销刚刚分配的所有设备 */289 for (n = from; n < to; n = next) {290 next = MKDEV(MAJOR(n)+1, 0);291 /* [CGW]: 对应的内存空间 */292 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));293 }294 295 /* [CGW]: 返回这个分配失败的设备指针 */296 return PTR_ERR(cd);297 }298 299 /**300 * alloc_chrdev_region() - register a range of char device numbers301 * @dev: output parameter for first assigned number302 * @baseminor: first of the requested range of minor numbers303 * @count: the number of minor numbers required304 * @name: the name of the associated device or driver305 *306 * Allocates a range of char device numbers. The major number will be307 * chosen dynamically, and returned (along with the first minor number)308 * in @dev. Returns zero or a negative error code.309 */310 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,311 const char *name)312 313 {314 struct char_device_struct *cd;315 /* [CGW]: 自动分配一个设备,因为主设备号为0 316 * 以baseminor为基址,分配count个次设备号317 */318 cd = __register_chrdev_region(0, baseminor, count, name);319 /* [CGW]: 分配失败 */320 if (IS_ERR(cd))321 return PTR_ERR(cd);322 /* [CGW]: 返回设备号 */323 *dev = MKDEV(cd->major, cd->baseminor);324 return 0;325 }326 327 /**328 * register_chrdev() - Register a major number for character devices.329 * @major: major device number or 0 for dynamic allocation330 * @name: name of this range of devices331 * @fops: file operations associated with this devices332 *333 * If @major == 0 this functions will dynamically allocate a major and return334 * its number.335 *336 * If @major > 0 this function will attempt to reserve a device with the given337 * major number and will return zero on success.338 *339 * Returns a -ve errno on failure.340 *341 * The name of this device has nothing to do with the name of the device in342 * /dev. It only helps to keep track of the different owners of devices. If343 * your module name has only one type of devices it's ok to use e.g. the name344 * of the module here.345 *346 * This function registers a range of 256 minor numbers. The first minor number347 * is 0.348 */349 350 int register_chrdev(unsigned int major, const char *name,351 const struct file_operations *fops)352 353 {354 struct char_device_struct *cd;355 struct cdev *cdev;356 char *s;357 int err = -ENOMEM;358 359 /* [cgw]: 分配一个设备,次设备号为0~255 */360 cd = __register_chrdev_region(major, 0, 256, name);361 if (IS_ERR(cd))362 return PTR_ERR(cd);363 /* [cgw]:分配一个cdev结构体 */364 cdev = cdev_alloc();365 if (!cdev)366 goto out2;367 368 cdev->owner = fops->owner;369 cdev->ops = fops;370 371 /* [cgw]: 设置kobject的名字 */372 kobject_set_name(&cdev->kobj, "%s", name);373 /* [cgw]: 把kobject的名字kobj->name中的'/'替换成'!' */374 for (s = strchr(kobject_name(&cdev->kobj),'/'); s; s = strchr(s, '/'))375 *s = '!';376 377 /* [cgw]: 添加一个字符设备到系统*/378 err = cdev_add(cdev, MKDEV(cd->major, 0), 256);379 if (err)380 goto out;381 382 /* [cgw]: 设置char_device_struct中的cdev指针 */383 cd->cdev = cdev;384 385 return major ? 0 : cd->major;386 387 out:388 /* [cgw]: kobect 引用计数-1 */389 kobject_put(&cdev->kobj);390 391 out2:392 /* [cgw]: 释放刚注册的设备 */393 kfree(__unregister_chrdev_region(cd->major, 0, 256));394 return err;395 }396 397 /**398 * unregister_chrdev_region() - return a range of device numbers399 * @from: the first in the range of numbers to unregister400 * @count: the number of device numbers to unregister401 *402 * This function will unregister a range of @count device numbers,403 * starting with @from. The caller should normally be the one who404 * allocated those numbers in the first place...405 */406 407 void unregister_chrdev_region(dev_t from, unsigned count)408 {409 dev_t to = from + count;410 dev_t n, next;411 412 /* [CGW]: 注销所有从from到to的count个设备 */413 for (n = from; n < to; n = next) {414 /* [CGW]: 查找下一设备号*/415 next = MKDEV(MAJOR(n)+1, 0);416 if (next > to)417 next = to;418 /* [CGW]: 注销所有刚才注册的设备 */419 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));420 }421 }422 423 424 int unregister_chrdev(unsigned int major, const char *name)425 {426 struct char_device_struct *cd;427 /* [CGW]: 根据主设备号,找到对应设备列表项 */428 cd = __unregister_chrdev_region(major, 0, 256);429 /* [CGW]: 该设备项有效,并且被注册 */430 if (cd && cd->cdev)431 /* [CGW]: 注销该设备 */432 cdev_del(cd->cdev);433 /* [CGW]: 释放该设备占用的内存空间 */434 kfree(cd);435 436 return 0;437 }438 439 static DEFINE_SPINLOCK(cdev_lock);440 441 static struct kobject *cdev_get(struct cdev *p)442 {443 struct module *owner = p->owner;444 struct kobject *kobj;445 /* [cgw]:cdev_get uses try_module_get to attempt to increment that module's446 * usage count. If that operation succeeds, kobject_get is used to increment the447 * kobject's reference count as well---<Linux Device Drivers>448 * try_module_get(owner)增加owner (THIS_MODULE)引用计数449 */450 /* [cgw]: module使用计数+1 */451 if (owner && !try_module_get(owner))452 return NULL;453 /* [cgw]: kobj引用计数+1 */454 kobj = kobject_get(&p->kobj);455 /* [cgw]: kobj指针返回失败 */456 if (!kobj)457 /* [cgw]: module使用计数-1 */458 module_put(owner);459 460 return kobj;461 }462 463 void cdev_put(struct cdev *p)464 {465 /* [cgw]: cdev指针不为空 */466 if (p) {467 /* [cgw]: 获得模块指针 */468 struct module *owner = p->owner;469 /* [cgw]: kobj引用计数-1 */470 kobject_put(&p->kobj);471 /* [cgw]: module使用计数-1 */472 module_put(owner);473 }474 }475 476 /*477 * Called every time a character special file is opened478 */479 int chrdev_open(struct inode * inode, struct file * filp)480 {481 struct cdev *p;482 struct cdev *new = NULL;483 int ret = 0;484 485 /* [cgw]: 进入临界区 */486 spin_lock(&cdev_lock);487 /* [cgw]: 从inode中得到一个字符设备cdev指针 */488 p = inode->i_cdev;489 /* [cgw]: struct cdev指针为空 */490 if (!p) {491 struct kobject *kobj;492 int idx;493 /* [cgw]: 进入临界区 */494 spin_unlock(&cdev_lock);495 /* [cgw]: 看看cdev_map的probes[inode->i_rdev]链表是否有inode->i_rdev这个设备496 * 并返回这个设备的kobj497 */498 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);499 /* [cgw]: kobj为空,错误 */500 if (!kobj)501 return -ENXIO;502 /* [cgw]: 根据返回的kobj,找出包含这个kobj的struct cdev指针 */503 new = container_of(kobj, struct cdev, kobj);504 /* [cgw]: 进入临界区 */505 spin_lock(&cdev_lock);506 /* [cgw]: 从inode中得到一个字符设备cdev指针 */507 p = inode->i_cdev;508 /* [cgw]: struct cdev指针为空 */509 if (!p) {510 /* [cgw]: 把这个struct cdev指针填装到inode->i_cdev */511 inode->i_cdev = p = new;512 /* [cgw]: 记录对应的索引 */513 inode->i_cindex = idx;514 /* [cgw]: 把inode->i_devices插入到p->list */515 list_add(&inode->i_devices, &p->list);516 /* [cgw]: 清除new指针 */517 new = NULL;518 /* [cgw]: 返回cdev中kobj指针为空,错误 */519 } else if (!cdev_get(p))520 ret = -ENXIO;521 /* [cgw]: 返回cdev中kobj指针为空,错误 */522 } else if (!cdev_get(p))523 ret = -ENXIO;524 /* [cgw]: 退出临界区 */525 spin_unlock(&cdev_lock);526 /* [cgw]: 实际上是cdev->kobj引用计数-1,module使用计数-1 */527 cdev_put(new);528 if (ret)529 return ret;530 /* [cgw]: module使用计数+1,并返回cdev->ops指针 */531 filp->f_op = fops_get(p->ops);532 /* [cgw]: filp->f_op指针为空,失败 */533 if (!filp->f_op) {534 /* [cgw]: 实际上是cdev->kobj引用计数-1,module使用计数-1 */535 cdev_put(p);536 return -ENXIO;537 }538 /* [cgw]: 调用filp->f_op->open,打开的是用户驱动程序中定义的539 * file_operations中的open函数540 */541 if (filp->f_op->open) {542 /* [cgw]: 上锁 */543 lock_kernel();544 /* [cgw]: 调用filp->f_op->open */545 ret = filp->f_op->open(inode,filp);546 /* [cgw]: 解锁 */547 unlock_kernel();548 }549 /* [cgw]: 调用filp->f_op->open失败 */550 if (ret)551 /* [cgw]: 实际上是cdev->kobj引用计数-1,module使用计数-1 */552 cdev_put(p);553 554 return ret;555 }556 557 void cd_forget(struct inode *inode)558 {559 /* [cgw]: 进入临界区 */560 spin_lock(&cdev_lock);561 /* [cgw]: 从链表删除一个inode->i_devices节点,562 * 并重新初始化这个链表563 */564 list_del_init(&inode->i_devices);565 /* [cgw]: inode->i_cdev指针清0 */566 inode->i_cdev = NULL;567 /* [cgw]: 退出临界区 */568 spin_unlock(&cdev_lock);569 }570 571 static void cdev_purge(struct cdev *cdev)572 {573 /* [cgw]: 进入临界区 */574 spin_lock(&cdev_lock);575 /* [cgw]: 测试cdev->list这个链表是否为空576 * 577 */578 while (!list_empty(&cdev->list)) {579 struct inode *inode;580 /* [cgw]: 找出包含cdev->list的struct inode结构体的指针 */581 inode = container_of(cdev->list.next, struct inode, i_devices);582 /* [cgw]: 从链表删除一个inode->i_devices节点,583 * 并重新初始化这个链表584 */585 list_del_init(&inode->i_devices);586 /* [cgw]: inode->i_cdev指针清0 */587 inode->i_cdev = NULL;588 }589 /* [cgw]: 退出临界区 */590 spin_unlock(&cdev_lock);591 }592 593 /*594 * Dummy default file-operations: the only thing this does595 * is contain the open that then fills in the correct operations596 * depending on the special file...597 */598 599 const struct file_operations def_chr_fops = {600 .open = chrdev_open,601 };602 static struct kobject *exact_match(dev_t dev, int *part, void *data)603 {604 struct cdev *p = data;605 /* [cgw]: 返回cdev中kobj成员指针 */606 return &p->kobj;607 }608 609 static int exact_lock(dev_t dev, void *data)610 {611 struct cdev *p = data;612 /* [cgw]: data中kobj引用计数+1,并返回kobj指针 */613 return cdev_get(p) ? 0 : -1;614 }615 616 /**617 * cdev_add() - add a char device to the system618 * @p: the cdev structure for the device619 * @dev: the first device number for which this device is responsible620 * @count: the number of consecutive minor numbers corresponding to this621 * device622 *623 * cdev_add() adds the device represented by @p to the system, making it624 * live immediately. A negative error code is returned on failure.625 */626 627 int cdev_add(struct cdev *p, dev_t dev, unsigned count)628 {629 /* [cgw]: 分配一个dev设备号给p->dev */630 p->dev = dev;631 /* [cgw]: 分配count个连续的次设备号632 * 这里实际是分配count设备,只是次设备号不一样,主设备号都一样633 */634 p->count = count;635 /* [cgw]: 把新加入的设备填装到一个probe结构,并把这个probe插入到636 * 对应probes[MAJOR(dev)]链表,即probes[]中每一个元素都是一个链表637 */638 return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);639 }640 641 static void cdev_unmap(dev_t dev, unsigned count)642 {643 /* [cgw]: 从probes[MAJOR(dev)]链表中删除一个节点(probe) */644 kobj_unmap(cdev_map, dev, count);645 }646 647 /**648 * cdev_del() - remove a cdev from the system649 * @p: the cdev structure to be removed650 *651 * cdev_del() removes @p from the system, possibly freeing the structure652 * itself.653 */654 655 void cdev_del(struct cdev *p)656 {657 /* [cgw]: 从probes[MAJOR(p->dev)]链表中删除一个节点(probe) 658 * 659 */660 cdev_unmap(p->dev, p->count);661 /* [cgw]: kobj引用计数-1 */662 kobject_put(&p->kobj);663 }664 665 static void cdev_default_release(struct kobject *kobj)666 {667 /* [cgw]: 找到包含kobj的结构体struct cdev的指针 */668 struct cdev *p = container_of(kobj, struct cdev, kobj);669 /* [cgw]: 从cdev->list链表中删除cdev */670 cdev_purge(p);671 }672 673 static void cdev_dynamic_release(struct kobject *kobj)674 {675 /* [cgw]: 找到包含kobj的结构体struct cdev的指针 */676 struct cdev *p = container_of(kobj, struct cdev, kobj);677 /* [cgw]: 从cdev->list链表中删除cdev */678 cdev_purge(p);679 /* [cgw]: 释放这个cdev的内存空间 */680 kfree(p);681 }682 683 static struct kobj_type ktype_cdev_default = {684 .release = cdev_default_release,685 };686 687 static struct kobj_type ktype_cdev_dynamic = {688 .release = cdev_dynamic_release,689 };690 691 /**692 * cdev_alloc() - allocate a cdev structure693 *694 * Allocates and returns a cdev structure, or NULL on failure.695 */696 struct cdev *cdev_alloc(void)697 {698 /* [cgw]: 分配一个cdev结构体 */699 struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);700 701 /* [cgw]: 分配cdev结构体成功 */702 if (p) {703 /* [cgw]: 分配一个kobj.ktype结构体,指向&ktype_cdev_dynamic704 * 为这个驱动制定一个统一的行为,提供释放kobj的方法705 */706 p->kobj.ktype = &ktype_cdev_dynamic;707 /* [cgw]: 初始化链表,把这个cdev插入链表头 */708 INIT_LIST_HEAD(&p->list);709 /* [cgw]: 初始化kobject,每个对象都有一个kobject */710 kobject_init(&p->kobj);711 }712 return p;713 }714 715 /**716 * cdev_init() - initialize a cdev structure717 * @cdev: the structure to initialize718 * @fops: the file_operations for this device719 *720 * Initializes @cdev, remembering @fops, making it ready to add to the721 * system with cdev_add().722 */723 void cdev_init(struct cdev *cdev, const struct file_operations *fops)724 {725 /* [cgw]: cdev结构体清零 */726 memset(cdev, 0, sizeof *cdev);727 /* [cgw]: 初始化链表,把这个cdev插入链表头 */728 INIT_LIST_HEAD(&cdev->list);729 /* [cgw]: 分配一个kobj.ktype结构体,指向&ktype_cdev_default730 * 为这个驱动制定一个默认的统一的行为,提供恢复默认kobj的方法731 * 没有释放kobj内存空间732 */733 cdev->kobj.ktype = &ktype_cdev_default;734 /* [cgw]: 初始化kobject,每个对象都有一个kobject */735 kobject_init(&cdev->kobj);736 /* [cgw]: cdev->ops指向驱动程序中的file_operations结构体 */737 cdev->ops = fops;738 }739 740 741 742 743 static struct kobject *base_probe(dev_t dev, int *part, void *data)744 {745 if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)746 /* Make old-style 2.4 aliases work */747 request_module("char-major-%d", MAJOR(dev));748 return NULL;749 }750 751 void __init chrdev_init(void)752 {753 /*[cgw]: 初始化cdev_map变量 */754 cdev_map = kobj_map_init(base_probe, &chrdevs_lock);755 }756 757 /* Let modules do char dev stuff */758 EXPORT_SYMBOL(register_chrdev_region);759 EXPORT_SYMBOL(unregister_chrdev_region);760 EXPORT_SYMBOL(alloc_chrdev_region);761 EXPORT_SYMBOL(cdev_init);762 EXPORT_SYMBOL(cdev_alloc);763 EXPORT_SYMBOL(cdev_del);764 EXPORT_SYMBOL(cdev_add);765 EXPORT_SYMBOL(register_chrdev);766 EXPORT_SYMBOL(unregister_chrdev);767 EXPORT_SYMBOL(directly_mappable_cdev_bdi);
原标题:char_dev.c 添加中文注释
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